I have heard that the Rancho had a lower compression ratio than the Bagheera and I wonderd about fitting those pistons. I did some calculations about how thick would the cylinder head gasket have to be to reduce the comp ratio enough. "Quite thick" was the result!

....and use a waterjet injection system. Saab used them on the Saab 900 Turbo (1987-1989; I think) and you can still get the AquaMist system for 500£ in Sweden. I know this relates more to detonation in the combustion chamber - but if it works on a turbo why not on a SuperCharger.

I have heard about the water injection system but know very little. How does it work? What sort of pump and nozzles? When does it inject the water? Maybe the same time as my intermittant lubrication system?

What about the electronic detonation detection devices? They reduce the igntion advance I understand.

Lanng, I would avoid saying that the Bagheera was underpowered. You need to compare the power/liter to other period cars. You'll see that when the car was issued in 1973, in was not bad.Simply, the weight is too high, the engine is too small and the design of the car let you believe that you miss 100 pk.

If you compare the Matra Bagheera 1.3 and the Ligier JS2, the power/liter ratio is the same. The Bagheera has a 1290 cc engine, the ligier has a 2950 cc maserati engine

Andy, If you want to decrease the compression, I have 2 easy solution for you.1) Remember Marcel Morel and his compressed Murena. He used a 1100 cc engine. Why ? Just a simple calculation. The cylinder head volume is kept the same (24 cc for the post 75 one and 20 for the early one)If you decrease the bore, you loose compression.So, use a 1100 as a basis but with the 70 rods2) Because of my 16V engines, I need to have custom built head gasket.They are currently being made, in coper. You can choose the thickness, even very thick

May I ask your advice please? (I have also posted this question in the Rancho section)..

I read that the Rancho had a lower compression ratio than the Bagheera with the same 1442cc engine. Someone told me that they achieved the lower compression by the use of a different piston height. Any advice would be very welcome.

I am tempted to fit the ex-Murena engine I already have but I need to do it quickly so as to have the blown car at NEC on November 13th.

Was there also a low comp 1600 engine perhaps on a Simca commercial vehicle?

They have said that the 1600 engine is not as strong as the smaller capacities particularly at high revs, but my Shorrock blower does not need to rev too hard and has a 6500rpm limit.

Thanks for the responses. I have made some progress today although I have not yet spoken to a man who might supply Rancho pistons!

I have the contact details of a man who can supply thick cylinder head gaskets. I'll call him tomorrow.

Several members have warned me that the 1600 engine is not very strong partially due to the non-symmetrical cylinder layout and crankshaft.

I am moving to the conclusion that I should stay with the 1442cc engine with Rancho pistons but with the stroke of 78mm reduced by crankshaft grinding to 77.2mm. This will give a reduced capacity of 1427cc and this when multiplied by the "forced induction factor" of x1.4 will give me a nominal capacity of 1995cc. This will satisfy the competition requirement to remain, after fitting the blower, within the original "Class" of 1401-2000cc. The reduced stroke will also reduce the compression ratio and any further reduction can be achieved by the use of a "decompression gasket".

The "decompression gasket" will cost about 120Euro and take 2 weeks to make. Specially made forged competition pistons are about 150Euro each (so Rancho pistons sound a good idea if they can be found!)

Just take a 1290 cc engine.Rebore it to fit the murena pistons.And (80.6 X 70) ... you get the 1428 cc engine.

Now about the gasket, I can have them made on order in coper, the thickness you want, for 50 €.I had some special gasket made and they are very nice.The postage cost will be cheaper than the 120 €.If you need, drop me a mail

I did some calculations a little while ago and from memory I needed an extra gasket of around 1.2mm thick (plus the standard gasket). That was probably based on a 1.6 Murena engine and 8.0:1 compression ratio.

JL said ... "..deck the pistons...". Do you mean remove some metal from the top of the pistons to get extra volume in the combustion chamber? That is not something I had considered. I wonder how much can be removed with harming the strength of the piston crown? Someone suggested that is how they made the Rancho low compression pistons.

Spyros said... "use Murena pistons in a bored-out 1293 block with a 70mm crankshaft." I've been thinking about this very neat solution which will give me exactly 2000cc after the "blower factor" but will this not have the same problems as Simca found in that there is not enough metal left between the cylinders? They went to (as I understand it) unevenly spaced cylinders and a different crankshaft. Could one use a 1.6 unevenly spaced crankshaft in the 1293 block? Hummmm. Perhaps I should take some measurements of our 1442 block when I take the head off to replace the gasket.

My thoughts yesterday of setting a new record for changing the head gasket have been set aside while we fit the blower. There is so much more space to work when the carbs and rocker cover have been removed.

Hi AndyDecking the pistons on a race engine (machining the crowns so that they all sit the same distance below the top of the block) is done to give you a balanced combustion chamber capacity which all helps smoother running etc and I seem to remember that there is plenty of meat on the piston crowns for machining - I also used to check the chambers in the head as well.Using a short stroke bored out 1294cc is a good way to go and if there is any doubt on block wall thickness just have some liners pressed in.The other thought is that you are now starting to spend enough money to make it worth thinking about having a set of custom pistons made.RegardsJohn

I agree with JL.If there is not enough meat you can decide to press liners in.But according to my calculation, you can use standard 80.6 pistons (Murena, Solara 1.6) or even the first reparation bore (+0.1) It is with the second reparation bore that you'll have issues.

Also, I don't understand why they produced the first reparation bore since if a 1590 engine is worn, you don't rmove enough by boring it this size. This means that you don't interfeer with Murena restorers. They can't use these pistons.

Still a consideration about the pistons tops : The 80.6 pistons (murenas & associated) are different from the previous ones: more hollow on the top.That would help lowering your compression.I'll try to find back the difference. I mesured it once.However, the previous pistons seems more resistant than these.3 years ago, I posted on this : http://www.bagheera-cafe.com/viewtopic.php?t=581&highlight=pistons